Catheterization is a relatively common medical procedure for treating drainage from a tube or duct. In the case of ureteral catheterization, a ureteral stent and/or a catheter may prevent or treat an obstruction affecting urine, produced in the kidney, flowing to the bladder. In most cases, stents allow or restore the free flow of urine from the kidney. In some instances, catheterization may also facilitate injection of liquids into the kidney. Typically, ureteral catheterization is performed by inserting a stent through a patient's urethra into the bladder.
Stents can be used to prevent closure of a passage, tube, or duct. The diameter of a stent can be expanded after being positioned within the patient, or they can be self-expanding such as in response to a change in temperature. In most cases, stents are designed to maintain their diameter after deployment and positioning. Where the stent is expandable, the material of the stent may be deformed after deployment. Alternatively, the stent may be manufactured from an elastic or shape memory material. In other cases, the stent may be compressed within a sleeve that prevents expansion of the stent until it has been properly positioned within the patient. After deformation, the stent is designed to remain in the deployed state.
Stents are often used to prevent closure or obstruction of the ureter. In some cases, the ureter may be blocked, for example by a kidney stone. While opening the ureter to allow resolution of a kidney stone may require only temporary positioning of the stent (days or weeks), other conditions may require the stent to remain in the ureter for longer periods of time, for example several months or longer. In some cases, stents may be placed within the ureter to prevent spasms and/or collapse of the ureter after an operation, for example, an operation to remove a kidney stone.
Guidewires may be used to position a stent. In some cases, a guidewire may be inserted into the ureter. The stent may be positioned about the guidewire and advanced until it is properly positioned. In some cases, a cystoscope may aid in positioning the guidewire. In many cases, fluoroscopy may be used to help ensure proper placement of the guidewire prior to advancing the stent.
In some cases, a stent may move after being positioned in the ureter. For example, the stent may move towards the kidney or bladder. Movement of the stent may arise for various reasons. For example, movement of the stent may be caused by routine activity and/or from strenuous physical activity by the patient. Movement of the stent may cause the ureter to partially collapse in regions of the ureter vacated by the stent and/or the stent to irritate or damage the bladder (e.g. the trigone) or kidney.
In order to prevent or reduce movement of a stent or (maintain patency), one or both ends of the stent may be curled in a pigtail, spiral, or J-shape (i.e., a curled retaining structure). The curled retaining structure may prevent or reduce migration of the stent within the ureter. Stents having a curled retaining structure at the kidney end of the stent (e.g. first end) may prevent the stent from moving towards the bladder. A curled retaining structure positioned at the bladder end of the stent (e.g. second end) may prevent movement of the stent towards the kidney. Additionally structures at the bladder end of the (e.g., a coil, string) may also aid in retrieval and removal of the stent.
Stents may cause or contribute to patient discomfort and pain. For example, patient discomfort and pain may be attributed to the stent irritating the trigone area of the bladder. Irritation of the trigone may occur when the stent or a retaining structure (e.g. curl retaining structure), contacts the trigone. The trigone (or trigonum) is a triangular-shaped region located on the floor of the urinary bladder, and is roughly defined by the opening of the urethra and the two ureteral orifices. The trigone is believed to be particularly innervated and, therefore, is especially sensitive to irritation caused by pressure, such as contact with a stent.
In some cases, stents may result in urine reflux. Urine reflux may occur when urine travels from the bladder to the kidneys in response to retrograde pressure. Retrograde pressure occurs in the bladder when attempting to void the bladder of urine, and may transmit urine or other fluids up the stent to the kidney. In response to this pressure, the lower portion of the ureter, proximal the bladder, normally closes during routine voiding of the bladder, but the presence of a stent or catheter may interfere with this closure. This may lead to irritation of the ureter as well as urine reflux.